The invention described herein relates to a method of purifying silane and more particularly to a method of purifying silane by photolyzing impurities therein and removing the photolysis products.
The technique of laser photochemistry are notable in their ability to selectively excite a single component in a mixture of isotopic or chemical species. The use of laser photochemistry for isotope separation has been well chronicled. However, only recently has attention been given to the possibility of chemical purification using such techniques. The photochemical separation of rare earth mixtures in solution has been achieved with both conventional and laser light sources. In the gas phase, laser-induced conversion of C.sub.2 H.sub.4 Cl.sub.2 and CCl.sub.4 into C.sub.2 H.sub.2, C.sub.2 H.sub.3 Cl, HCl, C.sub.2 Cl.sub.4, and C.sub.2 Cl.sub.6 in the presence of AsCl.sub.3 has been demonstrated. This technique could, in principle, lead to a means of purifying the AsCl.sub.3 of C.sub.2 H.sub.4 Cl.sub.2 and CCl.sub.4 if it were followed by a conventional physical separation process for the photolysis products.
Exceedingly high purity materials are required for the success of most semiconductor manufacturing processes. Impurity levels on the order of parts-per-billion can adversely affect device performance. As a result, a great deal of effort has been expended in devising methods of purification for materials used in the semiconductor industry. Heretofore, virtually all such schemes have shared a common feature: all of the material being purified is subjected to the same process. Since the impurities are normally present in only small amounts to begin with, it would be desirable to achieve further purification by some technique that would act only on the impurities while leaving the bulk of the reagent virtually unchanged.
Electronic grade silane (SiH.sub.4) is in demand for use in the preparation of semiconductor devices and solar cells. The principal impurities which degrade the performance of devices fabricated using electronic grade SiH.sub.4 are compounds which give rise to n- and p- type carriers. Thus, the presence of volatile compounds of the elements of Groups III and IV of the Periodic Table is especially pernicious. For SiH.sub.4, the major impurities of these types are phosphine (PH.sub.3), arsine (AsH.sub.3), and diborane (B.sub.2 H.sub.6).